Images captured by NASA’s spacecraft after the recent encounter with Comet Hartley 2 revealed a cosmic snow storm created by carbon dioxide jets spewing out tons of golf-ball to basketball-sized fluffy ice particles from the peanut-shaped comet’s rocky ends.
“This is the first time we’ve ever seen individual chunks of ice in the cloud around a comet or jets definitively powered by carbon dioxide gas,” said Michael A’Hearn, principal investigator for the spacecraft at the University of Maryland.
The presence of carbon dioxide explains why the smooth and rough areas scientists saw respond differently to solar heating, and have different mechanisms by which water escapes from the comet’s interior.
“Stereo images reveal there are snowballs in front and behind the nucleus, making it look like a scene in one of those crystal snow globes,” said Pete Schultz, EPOXI mission co-investigator at Brown University.
“The carbon dioxide jets blast out water ice from specific locations in the rough areas resulting in a cloud of ice and snow,” said Jessica Sunshine, EPOXI deputy principal investigator at the University of Maryland.
“Underneath the smooth middle area, water ice turns into water vapour that flows through the porous material, with the result that close to the comet in this area we see a lot of water vapour,” she added.
Engineers at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., have been looking for signs ice particles peppered the spacecraft.
“The EPOXI mission spacecraft sailed through the Hartley 2’s ice flurries in fine working order and continues to take images as planned of this amazing comet,” said Tim Larson, EPOXI project manager at JPL.
A more detailed analysis will determine how long this snow storm has been active, and whether the differences in activity between the middle and ends of the comet are the result of how it formed some 4.5 billion years ago or are because of more recent evolutionary effects.